Therapy apparatus



' electrostatic fields.

gical electrode may be connected to the output' Patented Nov. 9, 1943 assavco orr cs I .THERAPY APPARATUS Application September 2, 1941, Serial No. 409,166

I 10 Claims. (Cl. 128422) v tube oscillator, and an output circuit which is adapted to connect the source with the therapy load. The load is usually produced by treatment devices such as a pair of insulated electrodes of extended area which are applied to a patient'at spaced positions to subject a -pc'irtion of the patient to a high frequency electrostatic field, or it may comprise a cable which is wound about the patient to subject a portion of the patient to the combined action of the electromagnetic and As another example, a sur- Parallel tuned circuits at resonance are pro-' ductive of extremely high voltages when unloaded and require elaborate insulation. In fact, at extremely high frequencies the cost. of insulation makes the use of such circuits commercially impractical unless elaborate precautions are taken to prevent their being tuned to resonance when unloaded. Furthermore, the power source is usually set in operation before the load is connected to the apparatus.

It is well known that the magnitude of these no-load voltages at resonance can be decreased by increasing the ratio of the capacity to the inductance in the parallel tuned coupling circuit. This has the disadvantage that the efllciency of 1 load. We are also'able to use-an inductance having a ratio 01' reactanceto resistance: which is very high, that'is, an inductance with 'a-h igh Q.

These 'pre mniiritant; conditions to jrulflll since f they result in aneillcien'toutmitcircuit. At the the coupling circuit is low. 5 For etficient opera- .tion this ratio should be low. However, even Los Angeles, Calif., a

same time an output circuit so constructed can be operated with a minimum reaction on the source, wherefore the source can be operated with a minimum deviation from a given frequency. Further, such an output circuit may be satisfactorily used with a very stable source, such as a crystal controlled oscillator. This is of considerable importance at the present time in view of a growing tendency toward Federal restriction of therapy devices to a narrow band of fre quencies.

It is a primary object of this-invention to produce an output circuit which has a low capacity to inductance ratio and which does not produce inordinately high voltages when unloaded.

Another object of the invention is to provide an output, circuit which is incapable of being tuned to resonance when unloaded and which may be tuned to resonance when loaded'for a wide ,variety of loadings.

A further object oi the invention is to provide an output circuit which is incapable of being tuned to a frequency as high as the frequency or the source when unloaded, and which is tunable to the frequency of the source when loaded with a predominantly inductive load such as imposed by a normal short wave therapy load.

A further object of theinvention is to provide an eflicient output circuit which has little reaction on the radio frequency source, wherefore the source operates substantially at constant frequency- Our invention comprises a. parallel resonant output circuit suitably coupled to a. source of high radio frequency current for connecting the source to a therapy load such as condenser type electrodes, treatment cables or surgical electrodes. The parallel resonant output circuit comprises an inductance in parallel with a con denser. Either the condenser or inductance may be variable. The output circuitis further provided with out put" terminals connected to the ends of the inductance and adapted for connection to a treatment device, whereby the treat ment load 'along"with any other load produced thereby is connected in parallel with the inducta'nce. The constants of the output circuit are such that it'is impossible by varying the capacityofthe condenser or the value of the inductance to tune -the output circuit to the Ire- 'quency of the source when no treatment load is connected between the terminals. "The constantsjpf theoutput circuit are further-such that the presence of a normalv therapy load between the terminals results in'a load which is inductively reactive at the frequency of the source in parallel with the inductance. This lowers the total inductive reactance of the coupling circuit and makes it possible to tune the coupling circuit to the frequency of the source by varying the capacity of the condenser or the value of. the inductance. The output circuit may comprise loading coils or inductances connected between the terminals and the first-mentioned inductance in order to introduce the desired inductive reactance in parallel with the first-mentioned inductance when the treatment load is connected, if the treatment load does not introduce sumcient inductive reactance.

Further objects and'advantages of our invention are either specifically brought out in the ensuing description or will be apparent therefrom. 1

We have illustrated our invention in the accompanying drawing and referring thereto:

Fig. l is a schematic diagram of a short wave therapy circuit embodying our invention;

Fig. 2 is a graph illustrating the operation of our apparatus;

Figs. 3 and 4 are schematic diagrams illustrating alternative modes of coupling the output circuit to the source n Fig. 5 is a schematic diagram of an output circuit provided with a simple impedance matching network which may be used on extremely high frequencies, for example; and

Fig. 6 is a schematic diagram of an output circuit utilizing a fixed capacity and variable inductance.

Referring to Fig. 1 of the drawing, we have illustrated our invention in connection with a typical high frequency source or generating circuit such asa push-pull oscillator l which is surrounded by a dotted rectangle on the wiring diagram. This oscillator may be adapted to produce high frequency current at a wave-length of about 11.5 meters, for example. The source I is suitably coupled to an output circuit 'accord-' will be described only briefly. The source is shown as comprising a grid coil l0 having its opposite ends connected respectively to grids ,ll

P. C. Rawls.

and it of vacuum tubes is and I4 which are also provided with plates l5 and I5 and filaments I! and 18 respectively. The plates are connected between the filament side of thegrid resistor 22jand the midpoint of the tank coil [9.

The output circuit 2 of this invention is shown as comprising an output inductance 30 and a variable capacity condenser 3t connected in parallel with theoutput inductance 30. The inductance 30 and the condenser 3| comprise a paralleltuned circuit. The outputclrcuit 2 is shown coupled to th high frequency source I through the agency of coupling condensers 32 and 33 which "connect the respective [ends of the tank coil I! to the ends or the output inductance 30 Referring nowv to Figs. land ,2. and u'iolc bar-- tlcularly to Fig. 2, a curve '40 is shown which illustrates the relation between the capacity of the output condenser 3| and the resonant frequency of the output circuit when the output circuit is unloaded. The output condenser-3| is variable over a range between a minimum capacity valueCr and a maximum capacity value C2, and the output circuit may thus be tuned to resonance at any frequency lying between a high 1 frequency f1 and a low frequency In. The inductance of the coil 30 and the capacity of the condenser 3| are so chosen that the frequency 11 lies below the frequency of the source indicated at Is. For that reason it is impossible to tune the output circuit to resonance when it is unloaded. Thus no dangerously high voltages exist in the output circuit at such a time,

and it is also possible to connect the load tc the output circuit without the production of dangerous arcs. Furthermore, the ratio of the capacity of the condenser 3| tothe inductance oi the coil 30 may be made very low, with resulting highefliciency of the output circuit. By using a high value of inductance it is possible to match higher impedance loads. Furthermore, the inductance 30 may have a high Q.

Our circuit further comprises a loading portion 3 which includes load ng coils 34 and 3! the respective ends of which are connected tc the respective opposite sides of the inductance 30 and to output terminals 38 and 31. The coil: 34 and 35 are inductively reactive at the frequency of the source.

A treatment load 4 is shown connected between the terminals 36 and 31 and is indicated in dot-dash lines. The treatment load 4 produces a current flow in the loading coils l4 and 35 and may either be predominantly capacitatively or predominantly inductively reactive. The treatment load is produced by the current flow through the connections to the treatment devices (which may comprise cables, pads, surgicai appliances or other electrotherapeutical orelectrosurgical appliances) and the load produced by the current flow through the patient. Various examples-oi such loads are illustrated in U. S Patent No. 1,945,867, issued February 6, i934, tc

Until the treatment load is effective, that is until it actually imposes a load on the circuit there is no effective current flow through. the coils 34 and 35 and they produce no loading Hence, they have no appreciable efiect on the circuit, since they do not constitute a load. Ir this unloaded condition, therefore, the .outpu circuit operates according to curve 40.

The values of the loading coils 34 and 35 are so chosen that a normal treatment load will impose an inductively reactive load on the output circuit. This reactance is in parallel with the inductance 30 and eflectively lowers the reactance in parallel with the condenser 3| in the output circuit. The value of the inductance It is such that when a normal treatment load i: connected between terminals 36 and 31, the output circuit may b turned to the frequency 01 the source by adjusting the condenser to a value within its capacity range. I v

Dotted curve 4| in. Fig. 2 illustrates the relation between the. capacity .of the output condenser 3| and the resonant frequency of the output circult when the treatment load is connected be- ",tween the, output terminals for a value of treat- .men'tload lying within the'normal range. From a M u e 41 ttmi e e n t a t output circuit is tunable between a frequency in, and a frequency is which lie respectively below and above the frequency of the source fa. Furthermore, the output circuit may .be tuned .to resonance at source frequency is.

It should be obvious that the output circuit may be coupled to the source in any one of a .ends of the inductance 52. Except for the type of coupling, in Fig. 1.

In Fig. 4 an arrangement is shown which employs link coupling. A portion of a source is shown at 60 and comprises a tank coil 61 inductively coupled to a link coupling coil 62 which is connected to a second link coupling coil 63. An

this circuit may be the same as shown voutput circuit according to our invention is indicated at 64 and comprises an'inductance 65 which is inductively coupled to the coil 63. The output circuitmay otherwise be the same as illustrated in Fig. 1. e

It is to be pointed out that it is not always necessary to employ loading coils to cause the treatment load to impose an inductive load on the output circuit. The load a given treatment device itself imposes'on the system will vary with frequency. For example, we have found the circuit illustrated in Fig. 1 quite satisfactory for all normal treatment loads encountered at 11.5 meters. However, at a higher frequency, for example 5.75 meters, the inductive reactance of some normal treatment loads is so high that loading coils are not necessary.

In Fig. an output circuit according tothis invention is illustrated at "and is shown as comprising an inductance ll suitably coupled to a.

source not shown, and a variable capacity 12' in parallel with the inductance I l The apparatus This source is shown as comprising a one indicated at 3la. The variable inductance 30a may be constructed in any of the manners,

well known in the art. For example, the inductance may be tuned by a slider moving in a helical path along the coil turns as is commonly used in transmitter practice;

With the output circuit 2a substituted for the output circuit 2 of Fig. 1, the resonant frequency of the output circuit 2a is tunable between a first frequencyand a second higher frequency as the inductance of coil 30;; is varied between its highest and lowest values. The values of inductance and capacity are such that with the treatment load disconnected, said second frequency is lower than the frequency of the source I. Hence it is impossible by varying the value of the inductance 30a to bring the output circuit to resonance with the source! when the treatment load 4 is disconnected.

As pointed out previously, connection of the treatment load t to the terminals 36 and 31 is reflected in the output circuit as an inductively reactive load either because the treatment load is. predominantly inductively reactive or because the combination of the loading device '3 and load 4 is inductively reactive. Thus, connection of theload a has the sam effect a the placing of an inductance in parallel with the inductance 30a and decreases the total inductance in parallel with the condenser 3la. As a result, the output circuit is now tunable to a higher frequency than it was before and the constants of the circuit are preferably such that the output circuit is tunable to the frequency of the source I.

It should be obvious that the variable condensers in the output circuits illustrated in Figs. 3, 4 and 5' may be replaced by fixed ones and the corresponding parallel fixed inductancesmay be replaced by variable ones. In every case the same advantages as realized with variable condensers will be obtained, that is, it will be impossible to tune the output circuit to the resonance with the high frequency source until the treatment load is connected.

Having now described and illustrated particu lar forms of our invention, we wish it to be understood that our invention is not limited to the is shown provided with two sets of output terminals, I3 and 14, and I5 and 16,'respectively. The first set is connected directly to the opposite sides of the inductance 'llwhile th second set is connected to the'ends of the coil 1| through loading coils 11 and 18. Thus highly inductive treatment loads are connected between terminals 13 and i4 and capacitative or low inductance loads are connected between terminals 15 and,

Under such circumstances a fixed condenser ele-' ment may be employed in the place of-- the vari able one. In Fig. 6 the output circuit 2 of Fig. 1 is indicated at 2a as modified for inductive tuning. Thus the fixed inductance 30 has been replaced by a variable inductance 30a and the variable condenser 3l has been replaced by a fixed specific forms or arrangements herein described and shown, but rather to the contemplation expressed by our claim.

We claim:

1. A high frequency electrotherapy apparatus provided with ahigh frequency generating cir-" cuit means stabilized at a given frequency level; and an output circuit, means coupled to said generating circuit means including an inductance element and having a resonant frequency different from said given frequency level, said output circuit means including a capacity element parallel connected to said inductance element and output terminals adapted to receive, in parallel connection to said inductance and capacity elements, a treatment-device adapted to impose a given inductive load'upon said output circuit means, one of said elements being variable,.the value of said elements, with respect to such inductive load, being such that said output circuit remains out of resonance with said generating circuit means at all values of said one element when said treatment device is unconnected, and being such that said output circuit means can be brought into resonance with said generating circuit means through the agency of said one variable eIement when said treatment device is connected.

2. A high frequency electrotherapy apparatus comprising: a current source adapted to supply electrical current at a high radio frequency; and an output circuit coupled to said source, said output circuit comprising an inductance element, a capacity element connected in parallel with said inductance element and output terminals connected in parallel with said inductance element, one of said elements being variable over a range between a maximum and a minimum value, the value of the other of said elements being such that said output circuit is resonant to a frequency lower than the frequency of said source when said one element has a minimum value, said output circuit being resonant to the frequency of the source when said one element has a value in said range and a normal treatment load is connected between said terminals.

3. A high frequency electrotherapy apparatus provided with a high frequency generating circuit means stabilized at a given frequency level; and an output circuit means coupled to said generating circuit means including an inductance and having a resonant frequency different from said given frequency level, said output circuit means including a variable capacity parallel connected to said inductance and output terminals adapted to receive, in parallel connection to said inductance and said variable capacity, a treatment device adapted to impose a given inductive load upon said output circuit means, the value of said inductance and such capacity, with respect to such inductive load, being such that said output circuit remains out of resonance with said generating circuit means at all values of said variable capacity when said treatment device is unconnected, and being such that said output circuit means can be brought into resonance with said generating circuit means through the agency of said variable capacity when said treatment device is connected.

4. A high frequency electrotherapy apparatus comprising: a currentsource adapted to supply electrical current at a high radio frequency; treatment circuit means including a treatment device adapted for application to -a patient, said circuit means comprising an inductively reactive load at the frequency of said source when said "device is operatively associated with a patient and a negligible load when said device is not operatively associated with a patient; and an output circuit associating said treatment circuit means with said source, said output circuit comprising an inductance in parallel with said treatment circuit means and a variable capacity condenser in parallel with said inductance, the relative values of said inductance and-said capacity being such that said output circuit is tunable to resonance when said treatment device is operatively associated with a patient and is not tunable to resonance when said treatment device is not operatively associated with a-patient.

5. A high frequency electrotherapy apparatus comprising: a current source adapted to supply electrical current at a high radio frequency; and an output circuit coupled to said source, said output circuit comprising an inductance, a capacity connected in parallel with said inductance and output terminals connected in parallel with said inductance, said capacity being variable over a range between a maximum and a minimum value, the value of said inductance being such that said output circuit is resonant to a frequency lower than the frequency of said source when said capacity is at said minimum value, said output circuit being resonant to the frequency of said source when said capacity has a value within said range and a normal treatment load is connected between said terminals.

6. An apparatus as set forth in claim 5, comprising in addition, loading coils connected be tween said terminals and said inductance.

7. In an electrotherapy apparatus having a source of high radio frequency current, an output circuit coupled to said source and comprising: an inductance; a capacity connected in parallel with said inductance and being capable of variation over a range between a low value and a, high value; and output terminals connected to the opposite sides of said inductance, the value of said inductance being such that said output circuit is resonant to a frequency lower than the frequency of said source when no load is connected between said terminals and said capacity is at said minimum value, said output circuit being resonant to the frequency of said source when a normal treatment load is connected between said terminals and said capacity has a value within said range.

8. An apparatus as set forth in claim 7, said outputcircuit further including a loading coil connected between each of said terminals and the ends of said inductance.

9. In an electrotherapy apparatus having a source of high radio frequency current, an output circuit coupled to said source and comprising: an inductance; a capacity connected in parallel with said inductance and being capable of variation over a range between a low value and a high value; and output terminals connected to the opposite sides of said inductance,-the value of said inductance being such that said output circuit is resonant to a frequency lower than the frequencyof said source when no load is connected between said terminals and said capacity is at said minimum value, said output circuit being resonant to the frequency of said source when a normal predominantly inductively reactive treatment load is connected between said terminals and said capacity has a value within said range. 10. A high frequency electrotherapy apparatus provided with a high frequency generating circuit means stabilized at a given frequency level; and an output circuit means coupled to said generating circuit means including a capacity and having a resonant frequency diflerent from said given frequency level; said output circuit means.

including a variable inductance parallel connected to said capacity and output terminals adapted to receive, in parallel connection to said variable inductance and said capacity, a treatment device adapted to impose a given inductive load upon said output circuit means, the value of said inductance and such capacity, with respect to such inductive load, being such that said output-circuit remains out of resonance with 'said generating circuit means at all values of said variable inductance when said treatment device is unconnected, and being such that said output 

